I think I should post the issue I'm encountering in this topic.
My kingdom(Swadia) has advanced the tech to level III which grants an access to tier II troops. However, when I tried to recruit troops at my own castle, the troops options for tier II show those of tier I. Therefore, I can't get any advanced troops and now nearly all kingdoms of Calradia are declared war with my kingdom. One of those kingdoms has more advanced troops than those of mine.